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Monitor lizard

life science Maturity 5-7 Next article →

Monitor lizards are a diverse group of reptiles belonging to the genus Varanus. They are the only living members of the family Varanidae. These lizards are found across Africa, Asia, and Oceania. One species has even become an invasive species in the southern United States. Scientists currently recognize about 94 different species. They are known for having long necks, powerful tails, and strong limbs with sharp claws.

Varanus phylogeny as of Brennan et al 2020 (UPDATE 5)
Varanus phylogeny as of Brennan et al 2020 (UPDATE 5)

Most monitor lizards are carnivores that hunt various prey. They eat insects, fish, birds, and small mammals. Some species even eat eggs or molluscs. While most are meat-eaters, a few species are different. For example, three arboreal species from the Philippines—Varanus bitatawa, V. mabitang, and V. olivaceus—primarily eat fruit and vegetation.

Monitor lizards have a very specialized way of sensing their environment. Like snakes, they use a highly forked tongue to smell. The tongue collects molecules from the air or water. It then carries these molecules to the Jacobson's organ. This is a sensory organ located inside the skull. The forked shape allows them to sense scent boundaries in "stereo." This helps them pinpoint exactly where a smell is coming from. Interestingly, monitor lizards lack taste buds entirely.

Varanoid skulls
Varanoid skulls

These reptiles are also known for their unique biology and high energy. They have the highest standard metabolic rates of all living reptiles. This high metabolism supports their active-pursuit hunting style. Their hearts are also specialized to support this activity. Unlike most reptiles with three-chambered hearts, monitors have a well-developed ventricular septum. This structure completely separates the pulmonary and systemic sides of the heart during systole. This allows them to distribute oxygenated blood quickly to the body.

Komodo Dragon (15620549901)
Komodo Dragon (15620549901)

Many monitor lizards are also venomous. Anatomical studies show that their venom glands are located in the lower jaw. This is different from the way venom works in many snakes. The venom is complex and varies depending on the species' environment. Some species have anticoagulant venom that prevents blood from clotting. This causes wounds to bleed more than a normal cut. Other species, like the Komodo dragon, have neurotoxic venom. This type of venom can cause immediate paralysis in rodents.

Varanus niloticus ornatus
Varanus niloticus ornatus

History and naming provide interesting clues about these animals. The name Varanus comes from the Arabic word "waral," meaning "lizard beast." The English name "monitor" might come from their habit of standing on hind legs to watch surroundings. However, Carl Linnaeus may have named the Nile monitor in 1758 based on a mistake. He likely confused the German word "Waran" with the German word "warnen," which means to warn. In Australia, they are often called "goannas" due to confusion with other large lizards.

Monitor lizard in Kalahari
Monitor lizard in Kalahari

Monitor lizards vary greatly in size. The Komodo dragon is the largest living species. In contrast, some species like Varanus sparnus are much smaller. Even extinct relatives were massive. The extinct Megalania, or Varanus priscus, may have reached lengths of more than five meters.

Varanus priscus Melbourne Museum
Varanus priscus Melbourne Museum

These lizards show surprising levels of intelligence. Some rock monitors can distinguish between different numbers of snails up to six. Nile monitors have been observed cooperating to eat crocodile eggs. One lizard acts as a decoy to lure the mother crocodile away. Other monitors, like Komodo dragons, can recognize their human keepers. Some species even appear to engage in play by shredding leaves.

Monitor lizard at Kaziranga National Park
Monitor lizard at Kaziranga National Park
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🖼️ Images & Media (21)
File:Varanoid skulls.png
Varanoid skulls.png
File:Monitor lizard at Kaziranga National Park.jpg
Monitor lizard at Kaziranga National Park.jpg
File:Dada Panchal with monitor lizard 6 x 4.JPG
Dada Panchal with monitor lizard 6 x 4.JPG
File:Road kill lizard. India - Flickr - gailhampshire.jpg
Road kill lizard. India - Flickr -...
File:Varanus priscus Melbourne Museum.jpg
Varanus priscus Melbourne Museum.jpg
File:Varanus phylogeny as of Brennan et al 2020 (UPDATE 5).jpg
Varanus phylogeny as of Brennan et al...
File:Iguana and Indian monitor lizard.jpg
Iguana and Indian monitor lizard.jpg
File:Dumeril's Monitor Lizard (Varanus dumerilii) (Photo by Xavier MALLERET) (24237560651).jpg
Dumeril's Monitor Lizard (Varanus...
File:Clouded monitor 2.1.jpg
Clouded monitor 2.1.jpg
File:Varanidae - Varanus doreanus.JPG
Varanidae - Varanus doreanus.JPG
File:Varanus macraei - Reptilium Landau 01.jpg
Varanus macraei - Reptilium Landau 01.jpg
File:Varanus timorensis.jpg
Varanus timorensis.jpg

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